Apparatus for measurement of polarized distribution, polarizing filter for using therein and polarizing filter assembly

ABSTRACT

Disclosed are an apparatus for measurement of a polarized distribution, a polarizing filter for use of the apparatus and a polarizing filter assembly. 
     The apparatus for measurement of polarized distribution comprises an illuminating optical system for illuminating a subject to be examined by circularly polarized detecting light, and an image receiving optical system for receiving detected light from said subject illuminated by said circularly polarized detecting light. 
     The image receiving optical system includes a CCD element having an imaging provided integrally with a polarizing filter. The polarizing filter is composed of repetitions of unit platelets comprising polarizing micro-plates for decomposing the detecting light into first linearly polarized light components which are mutually perpendicular and polarizing micro-plates for decomposing the detecting light into second linearly polarized light components in a direction of crossing to the first linearly polarized light components.

CROSS-REFERENCE TO RELATED APPLICATION

This application in a continuation-in-part of application Ser. No.09/715,125, filed on Nov. 20, 2000, which has issued as U.S. Pat. No.6,540,357.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for measurement of apolarized distribution, a polarizing filter for using in the apparatusand a polarizing filter assembly.

2. Description of the Prior Art

In the field of medical ophthalmology, glaucoma is known as a diseaseresulting from excavation or deficiency in the nerve fiber layers ascaused by increased intraocular pressure, among others. At an advancedstage, glaucoma causes irreversible vision disorder, leading to loss ofsight. Therefore, early discovery of signs of glaucoma is regarded as anurgent task. However, the nerve fiber layers vary in thickness fromportion to portion on an ocular fundus and the progress of the defect ofthe nerve fiber layers is generally gradual until the morbid conditionbecomes severe, so that even when the fundus image is available as aresult of ophthalmography of the fundus of a patient at an early symptomstage, it is difficult for an oculist to judge, based on that image,whether there is a defective area in the nerve fiber layers.

Meanwhile, it is known that the nerve fiber layers are a birefringentsubstance showing different refractive indices according to thedirection of vibration (polarization) of light.

Thus, when the nerve fiber layers are irradiated with a certainpolarized laser beam, the polarized light components pass through thatlayer at different velocities, resulting in different times for passingthrough the nerve fiber layer for each of the components of thepolarized laser beam.

The magnitude of this phase difference is positively correlated with thethickness of the nerve fiber layers at the portion through which thelight has passed.

The polarized light is classified simply into linearly polarized light,circularly polarized light and elliptically polarized light according tothe quantity of phase difference between the polarized light components.

Utilizing this fact, a glaucoma diagnosis apparatus has been developedwhich converts a laser beam from a laser diode to the linearly polarizedstate by means of a polarizing filter having linearly polarizingcharacteristics, modulates this laser beam to circularly polarized lightusing a quarter wavelength plate, deflects that laser beam by means of ascanning unit to scan the ocular fundus therewith, detects the rate ofchange in phase difference of the light reflected from the ocular fundusand determines the thickness of the nerve fiber layers.

However, this glaucoma diagnosis apparatus in the prior art can onlyscan a certain narrow area of the ocular fundus and cannot examine awide area at a time. It has another problem that the data cannot beobtained as image information.

A further problem is that such a glaucoma diagnosis apparatus tends tobe expensive and is still hardly available for ordinaryophthalmologists.

Further, hitherto there is no an apparatus for measuring distribution ofa polarized light for a subject to be examined.

Accordingly, it is an object of the present invention, which has beenmade in view of the limitations of the related art discussed above, toprovide a glaucoma diagnosis apparatus capable of determining thethickness of the nerve fiber layers in a simple, easy and inexpensivemanner by improving the optical system of a currently existing retinalor fundus camera in common use.

It is another object of the present invention to provide an apparatusfor effective measurement of a polarized distribution of a subject to beexamined.

SUMMARY OF THE INVENTION

To accomplish the above object, an apparatus for measurement of apolarized distribution according to the present invention comprises: anilluminating optical system for illuminating a subject to be examined bycircularly polarized detecting light; and an image receiving opticalsystem for receiving detecting light from the subject which isilluminated by the circularly polarized detecting light.

The image receiving optical system includes a CCD element having animaging plane which is provided integrally with a polarizing filter.

In one embodiment, the polarizing filter is composed of repetitions of aset of unit platelets each comprising polarizing micro-plates fordecomposing the detecting light into first linearly polarized lightcomponents which are mutually perpendicular and polarizing micro-platesfor decomposing the detecting light into second linearly polarized lightcomponents which are in a direction of crossing with the first linearlypolarized light components and which are mutually perpendicular.

In other embodiment, the polarizing filter is composed of repetitions ofa set of unit platelets comprising polarizing micro-plates fordecomposing circularly polarized light into first linearly polarizedlight components which are mutually perpendicular and polarizingmicro-plates for decomposing said circularly polarized light into secondlinearly polarized light components in a direction of closing with saidfirst linearly polarized light components.

According to the present invention, a polarizing filter assembly isprovided. The assembly comprises a polarized filter and a CCD elementformed integrally with the polarized filter. The polarized filter iscomposed of repetitions of a set of unit platelets comprising polarizingmicro-plates for decomposing polarized light into first linearlypolarized light components which are mutually perpendicular andpolarizing micro-plates for decomposing said polarized light into secondlinearly polarized light components in a direction of closing with saidfirst linearly polarized light components.

The CCD element receives light passing through said polarized filter.

In one embodiment, the polarizing filter is formed in such a manner thatthe directions of the second linearly polarized light components whichare crossing with both of the first linearly polarized light componentsare at an angle of 45° with respect to both of the first linearlypolarized light components.

In one embodiment, each polarizing micro-plate corresponds to one pixelof said CCD element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external view of a typical fundus camera used in an ocularfundus photography.

FIG. 2 is a schematic view of an optical system of the fundus camerashown in FIG. 1.

FIG. 3 is an explanatory view of an imaging surface of the CCD camerashown in FIG. 2.

FIG. 4 is an explanatory view of a polarizing filter shown in FIG. 2.

FIG. 5 is an enlarged view of a unit platelet shown in FIG. 4.

FIG. 6 is a schematic view of the ocular fundus of a subject to beexamined.

FIG. 7 is an explanatory view illustrating the state of polarization ofthe reflected illuminating light from the ocular fundus of the subjectto be examined, wherein (a) shows the circularly polarized illuminatinglight, (b) the state of polarization of the illuminating light reflectedfrom the ocular fundus portion Hkl′ and (c) the state of polarization ofthe illuminating light reflected from the ocular fundus portion Hkl″.

FIG. 8 is a graphic view of the layer thickness data obtained in anexample.

FIG. 9 is a view of a modification of the optical system according to anembodiment 1 of the present invention.

FIG. 10 is a view of the optical system according to an embodiment 2 ofthe present invention.

FIG. 11 is a partial view of a modification of the optical systemaccording to the embodiment 2 of the present invention.

FIG. 12 is a view showing one embodiment in which the polarizing filteraccording to the present invention is applied to an apparatus formeasuring a polarized distribution.

FIG. 13 is a view showing the other embodiment in which the polarizingfilter according to the present invention is applied to the apparatusfor measurement of polarized distribution.

FIG. 14 is a plan view of an optical disc as the subject to be examinedshowing in FIGS. 12 and 13.

FIG. 15 is a view showing one example of a method for producing thepolarizing filter as shown in FIG. 4.

FIG. 16 is a partial enlarged sectional view of the polarizing filter asshown in FIG. 15.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[Embodiment 1 of the Invention]

FIG. 1 shows an example of a fundus camera Q to be used in a glaucomadiagnosis apparatus in connection with an apparatus for measuringdistribution of polarized light according to the present invention. InFIG. 1, 1-Q denotes a base, 2-Q a stand, 3-Q a main body, 4-Q ajoystick, 5-Q a CCD camera, 6-Q a jaw support, and 7-Q a foreheadstopper, and these constituents are already known.

With this fundus camera Q, a patient puts their jaw on the jaw support6-Q and their forehead on the forehead stopper 7-Q and looks at a fixedpoint in a predetermined direction by means of an internal fixationpoint lamp for fixation of patient's eye sight. Upon turning an imagingswitch 8-Q to “on”, the ocular fundus of a subject to be examined isilluminated by an illuminating optical system to be mentioned laterherein and a fundus image is recorded by the CCD camera 5-Q of animaging optical system to be mentioned later herein.

This CCD camera 5-Q is connected, for example, with a personal computer9 constituting a part of the glaucoma diagnosis apparatus and the fundusimage is stored in a frame memory of the personal computer 9. In placeof storing the fundus image in a frame memory of the personal computer9, the image may be recorded and stored in a bard disk, magnetic disk,floppy disk or optical magnetic disk.

An image display monitor 10 is connected with the personal computer 9and, upon operation by means of a mouse, keyboard or the like, thestored fundus image FB is displayed on a screen 11. On the screen, FCdenotes a mammilla, FD a macula of retina and FE a vascular vessel.

FIG. 2 shows the optical system of the fundus camera Q. In FIG. 2, 20denotes an illuminating optical system and 21 an imaging optical system.The illuminating optical system 20 comprises a xenon lamp 22 and ahalogen lamp 23 and the xenon lamp 22 and halogen lamp 23 are disposedin conjugated positions relative to a half mirror 24, and the xenon lamp22 and halogen lamp 23 are relayed by means of condenser lenses 25 and26 to the vicinity of a ring diaphragm X. This ring diaphragm X isrelayed, through a relay lens 27, a total reflection mirror 28A, a relaylens 28, a perforated mirror 29 and an objective lens 30, to thevicinity of the pupil of an eye 31 to be examined in the same manner aswith an ordinary fundus camera.

The imaging optical system 21 comprises an objective lens 30 facing theeye 31 to be examined, the perforated mirror 29, a focusing lens 32,relay lenses 33 (e.g., lens 33-1 and lens 33-2), a quick return mirror34, a CCD camera 5-Q and a photographic film 36. The symbol 5 a denotesthe imaging surface of the CCD camera 5-Q. The photographic film 36 andthe imaging surface 5 a are conjugated with respect to the quick returnmirror 34. On the occasion of taking a photograph on the film, the quickreturn mirror 34 is inserted into the optical path between the relaylenses 33 and CCD camera 5-Q, as indicated by a broken line and, on theoccasion of observation or photographing by the CCD camera 5-Q, themirror 34 is removed from the optical path.

Between the relay lens 28 and perforated mirror 29, there is detachablydisposed a polarizing unit 37 in the optical path of the illuminatingoptical system 20. This polarizing unit 37 is composed of a green filter38, a polarizing filter 39 having linearly polarizing characteristicsand a quarter-wave plate 40. During observation of the ocular fundus 41of the eye 31 to be examined, the polarizing unit 37 is kept removedfrom the optical path of the illuminating optical system 20.

The imaging surface 5 a of the CCD camera 5-Q is composed of a number ofpixels Gij (i=1, 2, . . . , m; j=1, 2, . . . , n), as shown in FIG. 3.In front of the imaging surface 5 a, there is integrally provided apolarizing filter 42. This polarizing filter 42 is constituted byarranging unit platelets Hkl (k=1, 2, . . . , m/2; I=1, 2, . . . , n/2)in the vertical and horizontal directions, as shown in FIG. 4. Each unitplatelet Hkl is composed of polarizing micro-plates Hkl1 and Hkl2adjacent to each other and dividing the reflected illuminating lightinto linearly polarized light components orthogonal to each other(transmitting linearly polarized light components crossing with eachother out of the reflected illuminating light) and polarizingmicro-plates Hkl1 and Hkl4 dividing the reflected illuminating lightinto linearly polarized light components crossing with both of thelinearly polarized light components mentioned above (transmittinglinearly polarized light components in the directions crossing with bothof the linearly polarized light components mentioned above), asenlargedly shown in FIG. 5. In this case, the directions of the linearlypolarized light components transmitted by the polarizing micro-platesHkl3 and Hkl4 are at an angle of 45° with respect to the linearlypolarized light components transmitted by the polarizing micro-platesHkl1 and Hkl2. The polarizing micro-plates Hkl1 and Hkl4 correspond tothe pixels Gij, respectively.

For observing the ocular fundus, the halogen lamp 23 is switched on, thepolarizing unit 37 is removed from the optical path of the illuminatingoptical system 20, and the ocular fundus 41 is illuminated withring-shaped illuminating light. The reflected illuminating light fromthe ocular fundus 41 is led, through the objective lens 30, the opening43 of the perforated mirror 29 and an imaging diaphragm Y, to thefocusing lens 32, and further to the imaging surface 5 a through therelay lenses 33 and polarizing filter 42 and forms an image on thesurface 5 a, and the fundus image FB is displayed on the screen 11.

In ophthalmography for glaucoma diagnosis, the polarizing unit 37 isinserted into the optical path of the illuminating optical system 20.When the xenon lamp 22 is caused to emit light, the illuminating lighttherefrom is led, through the condenser lens 25, half mirror 24,ring-form diaphragm X, relay lens 27, total reflection mirror 28A andrelay lens 28, to the polarizing unit 37. The green filter 38 transmitsgreen wavelength light, while it cuts light in other wavelength ranges.The green wavelength light is linearly polarized by the polarizingfilter 39. The linearly polarized green wavelength light is converted tocircularly polarized light by a quarter-wave plate 40. This circularlypolarized green wavelength light is reflected by the perforated mirror29 and passes through the objective lens 30 to become ring-shapedilluminating light and illuminates the ocular fundus 41 through thepupil of the eye 31 to be examined.

On the ocular fundus 41, as schematically shown in FIG. 6, optic nervefibers FF extend radially from the mammilla FC.

The birefringent characteristics of the optic nerve fibers FF differ bynature between the direction of running thereof and the directionperpendicular thereto.

When the eye is normal, the thickness of the nerve fiber layersincreases toward the mammilla FC and decreases as the distance from themammilla FC increases.

A portion on the ocular fundus irradiated with the circularly polarizedgreen wavelength light causes a change in phase difference owing to thebirefringent effect of the optic nerve fibers FF at that portion. Thechange in this phase difference increases as the thickness of the nervefiber layers FF increases.

The change in phase difference in circularly polarized light correspondsto the phenomenon that circularly polarized light changes intoelliptically polarized light, and the flatness of the ellipsecorresponds to the change in phase difference from circularly polarizedlight.

Thus, it can be said that the flatness of elliptically polarized lightis greater when the thickness of the nerve fiber layers FF is greater.

On the contrary, that portion of an ocular fundus which is deficient inoptic nerve fibers FF from some or other cause shows no birefringenteffect and the state of the circularly polarized light irradiated on theportion of ocular fundus is conserved as it is.

In this way, the illuminating light differing in polarized statedepending on the presence or the thickness of the nerve fiber layers FFas reflected by the ocular fundus 41 is led, through the objective lens30, perforated mirror 29 opening 43, imaging diaphragm Y, focusing lens32 and relay lenses 33, to the polarizing filter 42. If the unitplatelet Hkl of this polarizing filter 42 corresponds to a fundusportion Hkl′ shown in FIG. 6, then the reflected light from this fundusportion Hkl′ passes through the unit platelet Hkl and forms an image onthe four pixels Gij corresponding to that unit platelet.

On that occasion, the polarizing micro-plates Hkl1 to Hkl4 of the unitplatelet shown in FIG. 5 are disposed so that Hkl1 and Hkl2 respectivelycorrespond to the horizontal direction and vertical direction of theoptical system.

On the presumption that, at the ocular fundus portion Hkl′, thefluctuation in ocular nerve fiber layers thickness is slight within theportion, the received light output from the four polarizing micro-platesHkl1 to Hkl4 and from the corresponding four pixels Gij is regarded asthe received light output from one unit platelet Hkl and from thecorresponding pixels.

Here, suppose that the ocular fundus is irradiated with circularlypolarized light C shown in FIG. 7(a). (In FIG. 7, the horizontal axisand vertical axis respectively correspond to the directions of thepolarizing platelets Hkl1 and Hkl2.)

If, then, there are no optic nerve fibers FF at the fundus portion Hkl′,the reflected illuminating light from that fundus portion Hkl′ conservesthe state of circularly polarized light C.

Therefore, the reflected illuminating light passing through eachpolarizing micro-plate Hkl1 to Hkl4 of the unit platelet has the sameintensity and is received by the corresponding pixel Gij, and thereceived light outputs from the four pixels are the same.

When optic nerve fibers FF are present at that fundus portion Hkl′, thenthe reflected illuminating light from the fundus portion Hkl′ iselliptically polarized light C1 as resulting under the influence of thebirefingent properties of the optic nerve fibers FF, as shown in FIG.7(b). The flatness of the elliptically polarized light C1 isproportional to the thickness of the nerve fiber layers FF.

If the unit platelet Hkl of the polarizing filter 42 corresponds to thefundus portion Hkl′ shown in FIG. 6, then the reflected light from thatfundus portion Hkl′ passes through that unit platelet Hkl and makes animage on the corresponding four pixels Gij. If never fiber layers FF arepresent also at a fundus portion Hkl″, the reflected illuminating lightfrom that fundus portion Hkl″ becomes elliptically polarized light C2under the influence of the birefringent properties of the optic nervefibers FF, as shown in FIG. 7(c).

When the elliptically polarized reflected illuminating light C1 or C2entered the polarizing micro-plate Hkl1 of the unit platelet Hkl, thatmicro-plate inhibits other reflected illuminating light componentsexcept the polarized light component in the horizontal direction frompassing therethrough.

Similarly, when the elliptically polarized reflected illuminating lightC1 or C2 entered the polarizing micro-plate Hkl2, that micro-plateinhibits other reflected illuminating light components than thepolarized light component in the vertical direction from passingtherethrough. When the elliptically polarized reflected illuminatinglight C1 or C2 enters the polarizing micro-plate Hkl3 or Hkl4, thatmicro-plate inhibits other reflected illuminating light componentsexcept the polarized light component in the direction at an angle of 45°from the horizontal or vertical direction from passing therethrough.

Therefore, when the reflected illuminating light from the fundus portionHkl′ alone is taken into consideration, the received light output fromthe pixel corresponding to the polarizing micro-plate Hkl1 becomesmaximum, the received light output from the pixel corresponding to thepolarizing micro-plate Hkl2 becomes minimum, and the received lightoutput from the pixel corresponding to the polarizing micro-plate Hkl3or Hkl4 is roughly intermediate between the maximum and minimum output.

The explanation made herein is for the case in which the number ofmicro-plates is four. However, the shape of the ellipse can bedetermined from the received light outputs for at least three polarizedlight components, and the ratio between the minor axis and major axis ofthe ellipse can be determined therefrom. Therefore, the minimum numberof polarizing micro-plates required is three.

The ratio between the minor and major axis of the ellipse corresponds tothe flatness of the ellipse and there is a positive correlation betweenthe flatness of the ellipse and the thickness of the nerve fiber layers,so that by determining the flatness represented by the ratio between theminor and major axis of the ellipse for each fundus portioncorresponding to each unit platelet Hkl, it is possible to determinetherefrom the change in phase difference as caused at that fundusportion and thereby determine the thickness of the nerve fiber layers atthat portion. The computation for determining the layer thickness isconducted using the personal computer.

By reconstructing the fundus image based on the optic nerve fiber FFlayer thickness data obtained from the above computation for therespective unit platelets Hkl and displaying the game, it becomespossible to easily grasp the state of deficiency in optic nerve fiber FFlayer.

FIG. 8 is a graphic representation of the nerve fiber layers thicknessdata G1 obtained in an example for the respective fundus portions FX(cf. FIG. 6) resulting from radial division of the ocular fundustherearound with the mammilla FC as the center. The numerals 0 to 7given along the abscissa of the graph each corresponds to the directionof the fundus portion FX as shown in FIG. 6. The ordinate denotes thelayer thickness value.

The data given the symbol G2 are layer thickness data for a normalsubject and, by comparing the layer thickness data G1 with the layerthickness data G2, it becomes easier to grasp the state of deficiency inoptic nerve fibers FF.

It is desirable that such layer thickness data G2 for normal subjects bestored in a database as a collection of standard layer thickness datafrom which adequate standard data can be selected according to the age,race and other factors.

It is also recommendable to use a color CCD camera, for instance, tothereby use only received light output data for green wavelengthcomponents in computation.

FIG. 9 is a diagram illustrating a modification of embodiment 1 of theinvention, which has a constitution such that the polarizing filter 42is disposed at a conjugated position relative to the ocular fundus 41and a relay lens 56 is disposed between the polarizing filter 42 and theCCD camera 5-Q so as to make the polarizing filter 42 and imagingsurface 5 a conjugated, to thereby relayedly forming the fundus imageand the image from the polarizing filter 42 on the imaging surface 5 aby means of the relay lens 56.

The polarizing filter 42 is detachably disposed in the optical path ofthe imaging optical system 21. During observation, this polarizingfilter 42 is kept removed from the optical path of the imaging opticalsystem 21 and, on the occasion of taking a photograph, it is insertedinto the optical path of that imaging optical system 21.

By disposing the polarizing filter 42 detachably in the optical path ofthe imaging optical system 21 in that manner, it becomes possible toobserve the fundus image FB even when the polarizing unit 37 is disposedundetachably in the optical path of the illuminating optical system 20.

In this embodiment 1 of the invention as above illustrated, the greenfilter 38 is disposed in the polarizing unit 37. This is for the reasonthat the reflectivity of optic nerve fibers FF is greater at the greenwavelengths. While it is desirable that this green filter 38 beprovided, the present invention can be performed without providing sucha filter.

[Embodiment 2 of the Invention]

In the embodiment shown in FIG. 10, a polarizing filter 44 havinglinearly polarizing characteristics is provided between the imagingdiaphragm Y and focusing lens 32 in place of the polarizing filter 42comprising polarizing micro-plates differing in direction of linearlypolarized light and disposed in the optical path of the imaging opticalsystem 21 and, by rotating the polarizing filter 44 by 45° , the ocularfundus 41 is photographed four times for conducting nerve fiber FFlayers thickness analysis based on the four fundus images.

It is also possible to constitute this polarizing filter 42 as oneautomatically rotatable in response to the operation by thephotographer.

It is further possible to employ a constitution such that a mechanicallyrotatable polarizing filter 42 and a control device capable of settingan arbitrary angle of rotation of the polarizing filter and thecorresponding number of photos to be taken are provided forsynchronizing the rotation of the polarizing filter with the timing ofCCD photographing.

By employing such constitution, it is possible to record a requirednumber of images at respective angles of the polarizing plate in aninstant by one exposure operation.

When the ocular fundus portion corresponds to a certain pixel, thecircularly polarized illuminating light becomes elliptically polarizedlight under the influence of the birefringent properties of the opticnerve fibers FF at that portion. Out of components of this ellipticallypolarized light, only a component in the direction identical with thedirection of the linearly polarized light of the polarizing filter 44(component in a predetermined direction) is transmitted by thepolarizing filter 44 and other components of the reflected illuminatinglight are prevented from passing.

When this polarizing filter 44 is rotated by 90° from the predetermineddirection, this polarizing filter 44 transmits reflected illuminatinglight comprising a polarized light component orthogonal to the polarizedlight component in the predetermined direction (reflected illuminatinglight comprising a polarized light component in the minor axisdirection) while other polarized light components are inhibited frompassing by the polarizing filter 44.

Further, when this polarizing filter 44 is rotated to a 45° positionintermediate between the 0° direction and 90° direction, the polarizingfilter 44 transmits reflected illuminating light comprising a polarizedlight component in the 45° direction while other reflected illuminatinglight comprising a polarized light components are inhibited from passingtherethrough.

When nerve fiber layers FF run in the horizontal direction, a polarizedlight tends to flatten elliptically in the direction inclined by 45°from the horizontal direction, hence the received light output of thecorresponding pixel tends to become maximum in the 45° direction andminimum in the 135° direction and tends to become intermediate betweenthe maximum and minimum in the vertical (90°) direction.

Therefore, as mentioned above, when at least three received light outputdata are available for a pixel, the shape of the ellipse can bedetermined, hence the degree of flatness as represented by the ratiobetween the minor and major axis of the ellipse can be determined, sothat the nerve fiber layers thickness can be determined in the samemanner as in embodiment 1 of the present invention.

FIG. 11 illustrates a modification of embodiment 2 of the invention,according to the constitution of which a polarizing filter 44 isprovided in the imaging optical system 21, this polarizing filter 44 isnot rotated but polarized light beam splitters 45 to 47 differing inlinearly polarizing direction by 45° are provided in the optical path ofthe imaging optical system 21 and, at the same time, four CCD cameras 48to 51 are provided at positions conjugated with the ocular fundus 41 forsimultaneous photographing of the ocular fundus 41.

Since the method of computing the thickness of the nerve fiber layers FFis the same as mentioned hereinbefore, detailed description thereof isomitted.

According to the constitution shown in FIG. 11, the ocular fundus can bephotographed at one time and, therefore, the burden on the patient canbe alleviated.

[Embodiment 3 of the Invention]

FIG. 12 illustrates an example of application of a polarizing filter toan apparatus for measurement of polarized distribution.

In FIG. 12, reference numeral 50 is an illuminating optical system,reference numeral 51 is an original optical disc as a subject to beexamined. The illuminating optical system 50 generally comprises asemi-conductor laser 52, a collimator lens system 53, a ¼λ plate (¼wavelength plate) 54.

The optical disc 51 has a shape of plane as shown in FIG. 14 and istransparent in this embodiment.

Laser beam of linearly polarized light exited from the semi-conductorlaser 52 is formed into parallel beam by the collimator lens system 53.The parallel beam is formed into circularly polarized light by the ¼wavelength plate 54 after the parallel beam passes through a linearlypolarized light plate 53′ for forming ideal linearly polarized light.

The parallel beam formed in the circularly polarized light is directedas detecting light on the polarizing filter 42 constituting a portion ofthe image receiving optical system passing through the optical disc 51and then is imaged on the CCD camera 5-Q through the polarizing filter42.

The same structures as ones shown in FIGS. 4 and 5 may be used to thepolarizing filter 42. The polarizing filter 42 is provided on theimaging surface 5 a of the CCD camera 5-Q. The polarizing filter 42 iscomposed integrally with the CCD camera 5-Q to constitute a polarizingfilter assembly.

The polarizing filter 42 has the unit platelet Hkl as mentioned above(see FIG. 4). As described above, the unit platelet Hkl is composed ofthe polarizing micro-plates Hkl1 and Hkl2 for decomposing the detectinglight into first linear polarized light components which areperpendicular to each other and the polarizing micro-plates Hkl3 andHkl4 for decomposing the detecting light into second linear polarizedlight components which are in a direction of crossing with both of thefirst linear polarized light components and which are perpendicular toeach other.

In the embodiment, the directions of the linear polarized lightcomponents in the polarizing micro-plates Hkl3 and Hkl4 are at an angleof 45 with respect to the linear polarized light components in thepolarizing micro-plates Hkl1 and Hkl2.

The polarizing filter 42 is prepared by forming regularly latticepatterns 57 on a transparent substrate 66 by means of hot-etching and soon, as shown in FIGS. 15 and 16. In FIG. 15, reference numeral 58denotes a lattice groove pattern in direction of right oblique 45°numeral 59 a longitudinal lattice groove pattern, numeral 60 a laterallattice groove pattern and numeral 61 a lattice groove pattern indirection of left oblique 45.

Each of the lattice groove patterns 58 to 61 has a permeable ornon-permeable pattern in which the width p of pitch of groves is 0.1 μmthe depth d of the grooves is 0.1 μm, the width h of the grooves is 0.1μm.

These lattice groove patterns 58 to 61 act as micro-polarizing patternsbecause they are sufficiently small than a used wavelength.

The lattice groove pattern 58 corresponds to the polarizing micro-plateHkl4, the lattice groove pattern 59 the polarizing micro-plate Hkl2, thelattice groove pattern 60 the polarizing micro-plate Hkl1 and thelattice groove pattern 61 the polarizing micro-plate Hkl3.

Their polarizing micro-plates Hkl1 to Hkl4 each correspond to each ofthe pixels Gij in the imaging surface 5 a. In other words, onepolarizing micro-plate corresponds to one pixel of the CCD element.

An output of each of the pixels Gij is input in an analysis processingcircuit 55. The analysis processing circuit obtains a polarizingcharacteristic of a surface of the optical disc 51 corresponding to theunit platelet Hkl based on outputs of four pixels Gij corresponding tothe unit platelet Hkl and then obtains a characteristic of polarizeddistribution of the optical disc 51 by detecting the aforementionedpolarizing characteristic throughout the entire surface of the opticaldisc.

The characteristic of polarized distribution is output to a screen of amonitoring apparatus or printing apparatus.

In this embodiment, although the characteristic of the polarizeddistribution about a transparent subject such as the optical disc 51 isadapted to obtain, if the optical disc 51 is a type of reflection, theilluminating optical system 50 and polarizing filter assembly may bearranged as shown in FIG. 13. Because a phase is shifted in case ofreflection, a care to shift of phase should be taken in calculation ofthe characteristic of polarized distribution.

In the embodiment 3, since the characteristic of polarized distributionfor the surface of the subject can be measured at one time as a whole ofsurface without scanning the surface of the subject one point by onepoint and without rotating any polarizing detecting element, it ispossible to measure rapidly the characteristic of polarizeddistribution.

It is also possible to simplify an optical structure of the apparatusfor measuring the polarized distribution because the apparatus can beconstituted without using a moved mechanism.

As described above, in the embodiment 3, although the present inventionhas been applied to the optical disc as a subject, the subject is notlimited to the optical disc, a surface of a subject such as a compactdisc, a polarizing glass of a polarizing sun glass, a film duringrewinding mounted on a camera, a liquid, a liquid crystal disc, or asemi-conductive wafer.

Further, in the embodiment 3, although the semi conductive laser 52 hasbeen used as a light source of the illuminating optical system 60, aflush light source may be used.

Further, in the embodiment 3, although the unit platelet has beencomposed of the polarizing micro-plates Hkl1 to Hkl4 having fourdirectional linear polarized light components, it is possible to usepolarizing micro-plates having at least three directional linearpolarized light components.

What is claimed is:
 1. An apparatus for measurement of a polarizeddistribution comprising: an illuminating optical system configured toilluminate a subject to be examined by circularly polarized detectinglight; and an image receiving optical system configured to receivedetecting light from said subject illuminated by said circularlypolarized detecting light, said image receiving optical systemcomprising a charge-coupled device element having an imaging planeintegrally provided with a polarizing filter, said polarizing filterbeing comprising repetitions of a set of unit platelets each comprisingpolarizing micro-plates configured to decompose said detecting lightinto first linearly polarized light components that are mutuallyperpendicular and polarizing micro-plates configured to decompose saiddetected light into second linearly polarized light components that area direction of crossing with said first linearly polarized lightcomponents and which are mutually perpendicular.
 2. The apparatusaccording to claim 1, wherein the directions of said linearly polarizedlight components which are crossing with both of said linearly polarizedlight components are at angle of 45° with respect to both of said firstlinearly polarized light components, and each polarizing micro-platecorresponds to each pixel of said charge-coupled device element.
 3. Apolarizing filter comprising: repetitions of a set of unit plateletscomprising polarizing micro-plates configured to decompose circularlypolarized light into first linearly polarized light components that aremutually perpendicular and polarizing micro-plates configured todecompose said circularly polarized light into second linearly polarizedlight components in a direction of crossing with said first linearlypolarized light components, wherein the directions of said secondlinearly polarized light components which are crossing with both of saidfirst linearly polarized light components are at angle of 45° withrespect to both of said first linearly polarized light components, andeach polarizing micro-plate corresponds to each pixel of acharge-coupled device element.
 4. A polarizing filter assemblycomprising: a polarized filter comprising repetitions of a set of unitplatelets comprising polarizing micro-plates configured to decomposepolarized light into first linearly polarized light components that aremutually perpendicular and polarizing micro-plates configured todecompose said polarized light into second linearly polarized lightcomponents in a direction of crossing with said first linearly polarizedlight components; and a charge-coupled device element formed integrallywith said polarized filter and configured to receive light passingthrough said polarized filter.
 5. The polarizing filter assemblyaccording to claim 4, wherein each polarizing micro-plate corresponds toone pixel of said charge-coupled device element.
 6. The polarizingfilter assembly according to claim 4 or 5, wherein said polarizingfilter is formed in such a manner that the directions of said secondlinearly polarized light components which are crossing with both of saidfirst linearly polarized light components are at an angle of 45° withrespect to both of said linearly polarized light components.